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"Collagen"
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"Alverno College, MSOE Center for Biomolecular Engineering"

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Collagen

Collagen Structure

What is Collagen?

Collagen is one of the most abundant proteins in the human body and is located in the extracellular matrix as well as in connective tissue in the body. It can be found in our bones, muscles, skin tendons, hair and nails as well. Collagen acts as the glue that holds our bodies together and protects our insides from the dangers of the outside world. Collagen is a fibrous protein and is insoluble. With out this insolubility the collagen all over our body would dissolve when we stepped outside while it was raining, or even when we took showers. In nature there are about 16 different types of collagen. Often times in people though the collagen that is present is either type I, type II, type III or type IV. Multiple collagen molecules pack together to form what is called fibrils, which is long chains of the collagen molecule to form what we know as skin, hair, nails and so on. Collagen consists of two alpha one helices as well as an alpha two helical. The three main amino acids that are present in collagen are glycine, proline and a derivative of proline known as hydroxyproline. Hydroxyproline is very similar to proline but has an extra hydroxide group located on the ring of the amino acid.

The Types of Collagen in the Human Body

Type I: connective tissues of the skin, bone, teeth, tendons and ligaments.
Type II: Round fibers in cartilage.
Type III: connective tissues that shape and strengthen organs.
Type IV: Makes sheets that are found between layers of cells in blood vessels, muscles and eyes.

Fibrous Vs. Globular Proteins

Fibrous Proteins are very different from globular proteins. Not only do they look different, but they also have some different properties. Fibrous proteins are elongated proteins that are dominated by their secondary structure. Fibrous proteins are insoluble and also play an important role in structure and support of the body. Fibrous proteins can also be characterized by their repeated pattern throughout the entire structure that they are a part of. An example is the repeated structure of collagen on the skin.
Globular proteins are not long, as shown in the picture below. Globular proteins are very diverse and are soluble proteins that form tertiary and most times quaternary structures. For the most part globular proteins are chains of secondary structures with polypeptide chains attached to them. Examples of these proteins are enzymes, transport proteins as well as receptor proteins.

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Visual Representation of Fibrous and Globular Proteins

Amino Acid Groups in Collagen

There are three main amino acid groups in collagen. These amino acid groups include glycine, proline and hydroxyproline.

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Proline and Hydroxyproline Structures
Hydroxyproline Side Chain

Proline and Hydroxyproline in Collagen

Proline is a hydrophobic side chain that is in collagen. Proline is made up specifically of carbons and hydrogens, which also explains how it is so non polar. This is important because fibrous proteins need to be non polar to be able to be structural. Back to the idea of the collagen in your hair. If you were to take a shower your hair would dissolve into the water were it not for these hydrophobic side chains.
Hydroxyproline is a proline amino acid group with the addition of an alcohol. Though the structure of collagen will generally need to be non polar, the importance of this polar group is that it will enable collagen to be able to form strong hydrogen bonds that contribute to the strength of the collagen structure in general.

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Glycine Structure

Glycine in Collagen

Glycine is another non polar amino acid side chain. The importance of this non polar side chain is very similar to the importance of the non polar proline. This side chain helps to form the fibrous structure and helps to keep collagen from dissolving in water.

Which amino acid is the polar amino acid?

Glycine

Proline

Hydroxyproline

Proline in Collagen
Glycine in Collagen
Hydroxyproline in Collagen
Proline, Hydroxyproline and Glycine Shown in Collagen

What Exactly is Hydrogen Bonding?

Hydrogen bonding is not actually a bond at all. Instead it is an intermolecular force that attracts parts of a molecule to another. These hydrogen bonds are called hydrogen bonds because they occur when hydrogen is near nitrogen, oxygen or fluorine. The nitrogen, oxygen and fluorine would have a partial negative charge on them and the hydrogen would have a partial positive charge. These opposite charges are then attracted to one another like magnets, but they are never physically attached to one another like actual bonds are.

Hydrogen Bonding

Hydrogen Bonding

Hydrogen bonding helps collagen to form its 'tertiary' structure. The hydrogen bonds are very strong and keep the connective tissues in the body together. In the button below the hydrogen bonds are colored in green to show where these bonds take place in the molecule itself as well as where it can bind with hydroxyproline in other structures to form that tertiary structure.

Vitamin C

Vitamin C is necessary for the creation of hydroxyproline. This vitamin aids in creating the structure that tightly holds the collagen molecule together. Vitamin C binds together with proline and lysine to form a structure known as procollagen; this molecule is then used to produce hyrodroxyproline, and in turn collagen. Without a steady intake of vitamin C (roughly 90 mg for men and 75 mg for women daily) the body can undergo collagen deficiency, and it is possible for other complications such as scurvy to develop.

Scurvy

Scurvy is a disease caused by the deficiency of vitamin C in one's diet. As seen in the vitamin C blurb, this vitamin is essential in the production of hydroxyproline. Without the intake of vitamin C, no new collagen can be formed in the body; with no new collagen being formed to replace the old collagen the body begins to weaken. This casus the deterioration of the structural 'glue' that holds many systems within the body together. When collagen is not replaced�by the intake of vitamin C�major structural systems within the body begin to fail. This include: joints, strength of cartilage and tendons, blood vessels breaking open, gums getting weak, teeth falling out, and ultimately the failing of one's immune system. Some beginning symptoms of scurvy include: aching limbs, fatigue, skin papules, and corkscrew hair. A significant period of time without the intake of vitamin C must occur before scurvy becomes a serious threat.
Scurvy is not seen as much in today's society because of the access that many people have to fresh produce year round. It was seen in high numbers when sailors had no access to produce over long voyages. It became apparent that the vitamin C deficiency caused scurvy, and sailors began to eat limes, lemons, and other easily accessible fruits.

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